With recent significant developments in laser technology and its application in the field of ophthalmology, laser surgery has become the technique of choice for ophthalmic surgical applications, such as refractive surgery for correcting myopia, hyperopia, astigmatism, and so on, and procedures for treating and removing a cataractous lens. Laser eye surgery procedures generally employ an ultraviolet, an infrared, or a non-ultraviolet, ultrashort pulsed laser beam, and are performed while the patient is awake. The patient's head is stabilized using a headrest pillow, or the like. The laser surgical procedure typically requires that the patient's eye movement be stabilized. One approach to stabilize eye movement is to have the patient focus on a target during the procedure. These visual fixation targets typically include a light emitting diode (LED), which is optically positioned in front of or above the patient. Eye tracking systems have also been proposed to assist in eye fixation. Various systems and methods have been described for eye fixation, and separately for tracking eye movements. U.S. Pat. No. 6,299,307 issued to Oltean et al. discloses techniques for tracking eye movements. U.S. Pat. No. 6,406,473 issued to Shimmick et al. discloses techniques for providing eye fixation. These patents are herein incorporated by reference in their entirety.
It is desired that, when eye tracking is used, the patient interface be eliminated. The patient interface used in laser surgery is typically a rigid (glass lens) or a fluid (Balanced Salt Solution or “BSS”) interface comprised of a metal or rigid plastic conical adapter. The large end of the cone is a laser (fixation) mount. The small end of the cone fits against the corneal or scleral region of the eye with the aid of suction pressure. Instead of using such patient interface, it is desired that the eye be tracked using an eye tracking camera of the eye tracking system. The eye tracking system would then monitor the position and movements of the patient's eye. In order for the surgical process to proceed and continue, however, the patient's eye must remain generally fixed within a small central orientation. If the eye wanders, for example, outside of a 5 degree central region, the operation has to be halted until the eye returns to the eye tracking system's capture range and the range within which the laser can be successfully administered.
Current eye tracking and fixation systems and methods typically describe a single point fixation, fixed fixation, and/or central illumination target. In a single point fixation technique, light energy is directed toward the eye as a beam of light energy. The intersection of the beam of light energy with the eye comprises a light spot formed on the eye. Another technique may use a beam splitter to direct a plurality of light spots on the eye. In these techniques, however, the light spot or spots formed on the eye are fixed, and typically converged in the central region of vision, where visual acuity is the greatest. However, there may be certain situations and procedures that may cause the eye to lose its focus on the desired fixed point, thereby causing the eye to shift into undesirable positions. For instance, during cataract surgery, where lens fragmentation is carried out, the fragmented lens may hinder the patient's ability to fixate on the original fixed light spot. As a result, the patient's familiarity with the surroundings is eliminated, and he or she may not be able to hold his or her eye steady or to look in the direction necessary for the surgery.
Accordingly, improved systems and methods for guiding a patient's eye fixation during a laser ophthalmic surgery and/or ophthalmic diagnostic and measurement are desirable.